This proposal requests equipment necessary to extend preliminary studies combining intracerebral dialysis with behavioral measurement in freely moving rats during intravenous self-administration of cocaine. To that end facilities for in vivo microdialysis supported by an appropriate microsampling system will be established that will permit frequent sampling of synaptic concentrations of dopamine and its metabolites during 3 hour self-administration sessions. the purpose of these experiments will be to study the effects of self-administered cocaine on dopamine release in several terminal areas that have been implicated in cocaine reward and in the development of dependence and psychopathology associated with cocaine abuse. Synaptic levels of dopamine will be monitored at 5 minute intervals in the nucleus accumbens, prefrontal cortex and corpus striatum and compared to the animal's pattern of responding for the drug. Attempts will also be made to investigate specific changes in dopamine function after repeated as opposed to acute cocaine self administration. These studies have important implications for an understanding of critical circuitries in psychostimulant reward and dependence.